THE ENERGY CONTENT OF DRAGONFLIES (ODONATA) IN RELATION TO PREDATION BY FALCONS

Dragonflies and damselflies (Odonata) are important prey for many smal l falcons, and the recent expansion of the breeding range of the Hobby into eastern England has been associated with an increased availabili ty of dragonfly prey to juveniles. We have therefore measured the ener gy content and elemental composition of a range of common British drag onflies. Carbon and nitrogen contents were typical of aquatic inverteb rates and did not vary with dragonfly size, whereas ash content was si gnificantly reduced in larger species. The mean energy content of drag onfly tissue was 24.6 kJ/g (dry mass) and showed no significant variat ion between species. The energy content of an individual dragonfly ran ged from 0.8 to 9.4 kJ for the species examined in this study. Data on the energy requirements of free-living falcons suggest that a juvenil e Hobby in late summer could meet its daily energy requirement by capt uring between 75 and 90 Migrant Hawker or 200 to 250 Common Darter dra gonflies each day.